Field
Exemplary embodiments relate to a battery system of an electrically powered vehicle and more particularly to a battery system including a non-aqueous secondary battery for a vehicle drive power supply.
Description of the Background Art
A non-aqueous secondary battery containing a non-aqueous electrolyte as represented by a lithium ion secondary battery is employed as a vehicle drive power supply (a car-mounted power supply) for an electrically powered vehicle such as a hybrid car, an electric car, and a fuel cell car. As one of factors for increase in resistance of a non-aqueous secondary battery, what is called high-rate deterioration has been known, which is a phenomenon that increase in resistance is caused by variation (unevenness) in concentration of salt (an ion concentration) in an electrolyte as a result of continued charging or discharging at a high rate.
International Publication WO2013/046263 (hereinafter referred to as “Patent Document 1”) describes a value for evaluation of deterioration due to unevenness of an ion concentration in an electrolyte which is calculated based on a history of current values in charging and discharging of a battery and an integrated evaluation value found by integrating an excess over a threshold value and by correcting relaxation of unevenness of the ion concentration over time. Patent Document 1 describes a control for lowering a discharging electric power upper limit value of a secondary battery when the integrated evaluation value exceeds a threshold value (positive).
According to Japanese Patent Laying-Open No, 2014-3826 (hereinafter referred to as “Patent Document 2”), a common integrated evaluation value based on an evaluation value similar to that in Patent Document 1 is used, and when the integrated evaluation value is greater than a positive threshold value, determination as overdischarging is made and discharging electric power is restricted, and when the integrated evaluation value is smaller than a negative threshold value, determination as overcharging is made and charging electric power is restricted.